hemispheric lateralisation & split-brain research Flashcards
2 hemispheres
- left hemisphere
- right hemisphere
2 main language centres in left hemisphere are lateralised
- broca’s area in left front lobe
- wernicke’s area in left temporal lobe
what suggests LH is the analyser & RH is the synthesiser
RH can produce rudimentary words/phrases but contributes emotional context
some functions are not lateralised
eg. vision, motor & somatosensory areas appear in both hemispheres:
- motor area = brain is cross-wired (contralateral wiring) as RH controls movement on the left of the body
& LH controls the right - vision = contralateral & ipsilateral (opposite & same-sided) as each eye receives light from LVF & RVF
- the LVF of both eyes is connected to the RH & the RVF of both eyes is connected to the LH
‣ enables visual areas to compare different perspectives = aids depth perception - auditory input is similar to vision = variation from two inputs helps us locate the source of sounds
hemispheric lateralisation: AO3 +) research supporting lateralisation in the connected brain
E:
- fink et al. (1996) used PET scans to identify the brain areas active during a visual processing task
- when participants with connected brains asked to attend to global elements of the image regions of the RH
were more active
- when asked to focus on finer details specific areas of the LH often dominated
T: suggests (as far as visual processing is concerned) that hemispheric lateralisation is a feature of the
connected brain, as well as the split-brain
hemispheric lateralisation: AO3 -) idea that LH is the analyser & RH is the synthesiser may be incorrect
E:
- research suggests people don’t have a dominant side of their brain which creates a different personality
- nielsen et al. (2013) analysed brain scans from 1000+ people aged 7-29 & found people used certain
hemispheres for certain tasks (lateralisation evidence) but no evidence of a dominant side
T: suggests the notion of right/left-brained people is wrong
what is the split-brain operation
- severing connections between RH & LH (corpus callosum)
- used to reduce epilepsy
who conducted split-brain research
sperry (1968)
sperry’s (1968) research: procedure
- 11 people with split-brain operations studied
- image projected to RVF (LH) & same/different image projected to LVF (RH)
- ‘normal’ brain = corpus callosum would share information between hemispheres providing
complete picture
sperry’s (1968) research: findings
- when picture of object shown to RVF (LH), the participant could describe it
- if shown to LVF (RH), they said there was ‘nothing there’
- messages from RH couldn’t be relayed to language centres in LH
- could select matching object out of sight using left hand (RH)
- left hand could also select object most similar to object projected to LVF (RH) - eg. ashtray chosen when shown cigarette
- if pin-up picture shown to LVF there was an emotional reaction (eg. laugh) but usually reported
seeing nothing/flash of light
sperry’s (1968) research: conclusion
shows how certain functions are lateralised in the brain & support view that LH is verbal &
RH is ‘silent’ but emotional
sperry (1968) split-brain research: AO3 +) support from recent split-brain research
E:
- gazzaniga (luck et al. 1989) showed split-brain participants performed better than connected controls of
some tasks
- eg. faster at identifying odd one out from similar objects
- kingstone et al. (1995) - in normal brains, the LH’s better cognitive strategies are ‘watered down’ by inferior RH
T: supports sperry’s findings that ‘left brain’ & ‘right brain’ are distinct
sperry (1968) split-brain research: AO3 -) causal relationships are hard to establish
E:
- behaviour of sperry’s split-brain participants compared to neurotypical control group (none had epilepsy)
- major confounding variable as any differences observed between groups may be due to epilepsy not split-brain
T: some of unique features of split-brain participants cognitive abilities may be due to epilepsy (not split-brain)
